User guide

Application Guide | Gas detection in refrigeration systems
© Danfoss | DCS (MWA) | 2018.05 DKRCI.PA.S00.A1.02 | 520H12772 13
Number of gas detectors
in a facility
The requirements for the number of gas detectors
in a facility are not specifically stated in standards.
As general guideline:
• A gas detector can normally cover an area of
about 50-100 m
2
depending on the actual
condition of the space to be covered. In
spaces with several obstructions and lack
of ventilation the coverage is approx. 50 m
2
,
provided it is mounted near ceiling level or
near floor level depending on the refrigerant
density.
In non-obstructed spaces with good
mechanical ventilation, the coverage can be
increased up to approx. 100 m
2
.
• Machinery rooms:
It is recommended that gasdetectors are
placed above or at both sides of compressors
or other non-static parts of the system
or down wind of such equipment, in the
direction of continuously operating ventilation
extractors.
Where there are deep beams and lighter than
air refrigerants, it is recommended that the
detectors are mounted between pairs of beams
and on the underside of the beams.
If there is a continuous airflow in the
room a sensor/sensing point should
be located downstream from the last
potential leak source.
Calibration / test Calibration/test of gas detectors is extremely
important to ensure and document the proper
accuracy, responsiveness and operation of the
unit.
Gas detectors are subject to changes in the
measurement properties, dependent on the
operation time and/or exposure time. Therefore,
regular calibration is needed. The frequency
depends on various factors, however the
following four are of particular importance:
• Requirements of national legislation
• Recommended calibration interval
• Lifetime of the sensors
• The lifetime and calibration needs of
electrochemical sensors are highly affected
by exposure to the target gas, reducing the
lifetime and the calibration interval. For that
reason the concentrations of the target gas in
the area should also be considered.
Estimated life time
[year]
Min. recomended
calibration interval
[year]
Recomended test
interval**
[year]
SC Semi-conductor >5 1 1
EC Electrochemical >2* 1 1
P Pellistor 3-5 6 months 1
IR Infrared 15 5 1
* If the sensor is exposed to high or constant ammonia concentrations, the life time will be reduced.
An EC sensor remain functional above 30% of sensitivity.
** If calibration is performed, test is not required. However, when calibration interval is longer than the test interval, then a “bump”
test must be performed.
From a technically and safety point of view, the
sensors offered by Danfoss should be calibrated/
tested according to the stated intervals in the
table below.
IMPORTANT!
If national legislation requires
calibration/test with intervals shorter
(stricter) than stated in the table below,
these requirements must be followed.
Note: EN 378:2016 and ISO 5149 require gas
detectors to be checked on an annual basis.